Values For Enthalpies Of Formation Research Articles

DFT + U Study of Plutonium Hydrides with Occupation Matrix Control.

The magnetic order of plutonium hydrides (PuHx) has long been a subject of controversy, both experimentally and theoretically. The magnetic, structural, electronic, and thermodynamic properties of PuHx are investigated using Hubbard-corrected density functional theory (DFT + U), with U derived from linear response calculations. To address the issue of electronic metastable states within DFT + U, we employ an occupation matrix control method as well as allowing 5f orbitals to break the structural symmetry. This advanced computational approach establishes that the ground-state magnetic order for PuH2 is antiferromagnetic and that for PuH3 is ferromagnetic, consistent with Faraday and nuclear magnetic resonance experiments. Using the conventional hydrogen-vacancy model for PuHx, the hydrogen-content-induced magnetic transition and anomalous variation of the magnetic moment are successfully reproduced. In particular, the calculated transition point of x matches the experimental findings. Furthermore, the electronic configuration of the Pu atom in PuHx is determined to be 5f5, which is consistent with observations from X-ray photoemission spectroscopy. Our calculated values for enthalpy of formation, heat capacity, and entropy are in good agreement with experimental data, thereby validating the robustness of our theoretical framework.

Study of mechanical, optoelectronic, and thermoelectric characteristics of Be/Mg ions Based double perovskites A2FeH6 (A= Be, Mg) for hydrogen storage applications

This study addresses the hydrogen storage capabilities and mechanical, optoelectronic, and thermoelectric features of double perovskite hydrides A2FeH6 (A = Be, Mg). The structural aspects suggest the cubic symmetry of studied hydrides. The formation enthalpy value calculation has confirmed the structures' thermal stability. The gravimetric ratios of Be2FeH6 and Mg2FeH6 hydrides are 7.50 wt% and 5.43 wt%, respectively. The desorption temperatures are predicted to be 230.32 K and 208.67 K, respectively. The mechanical and thermophysical characteristics have been elaborated, which demonstrate mechanical stability, higher stiffness, ductile behavior, and higher temperature stability of both materials. The examined electronic properties have revealed band gap values of 2.89 and 3.08 eV, respectively. The optical properties have been assessed to predict the appropriateness of these hydrides for deployment in photovoltaic systems. The thermoelectric characteristics have been evaluated to examine the carrier transport mechanism and efficiency for converting heat into electricity. Finally, the investigated properties and hydrogen storage capacity of these compounds suggest that they are suitable for hydrogen storage and have the potential to play a key role in many energy generation applications.

First principles computation of novel hydrogen-doped CsSrO3 with excellent optoelectronic properties as a potential photocatalyst for water splitting

This research exhaustively inquired about the structural, photocatalytic, mechanical, and optoelectronic characteristics of the cubic perovskite CsSrO3−x Hx with the CASTEP code’s implementation of the GGA-PBE formalism. It aims to examine the characteristics of CsSrO3−xHx cubic perovskite with varied concentrations of substituents (x = 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4, 2.7, and 3.0). The stability and synthesizability of the compound are guaranteed by the values of elastic constants and negative formation enthalpies. As H-insertion increases, there are variations in the values of anisotropy and elastic moduli. A semiconductor’s wide bandgap narrows as dopant concentration rises, changing its nature from indirect to direct. The findings imply that the compound’s electronic characteristics can be altered through the application of dopants, rendering them appropriate for a range of optoelectronic uses. The inclusion of hydrogen caused the structural change from cubic to tetragonal and orthorhombic. The distortion caused the lattice parameters to vary in values. Tolerance factor lies in range of 0.7–1 that ensures structural stability of CsSrO3−x Hx. Our computed results reveal the anisotropic nature of our compound. The obtained bandgap for CsSrO3−xHx indicates that both O2 evolution and H2 reduction are allowed since the requisite redox potentials are satisfied. Photocatalytic properties of CsSrO2.4H0.6 reveals that it is the best doped system as a potential candidate for water-splitting photocatalysis, as it has equal effectiveness to both oxidation and reduction processes. The bandgap was shown to decrease from 5.33 eV to 2.812 eV at complete hydrogen insertion, which also had an impact on the material’s optoelectronic characteristics. All the optical considerations such as dielectric functions, refractive indices, extinction coefficients, optical reflectivity, absorption coefficients, and loss functions are also thoroughly explained. The material exhibits mechanical stability along with ionic and covalent bonding.

First principles insights into Cs2XAgCl6 (X= Sc, Y) compounds for energy harvesting applications

Herein, the investigation is presented to analyze the structural, electronic, optical, and thermoelectric features of Cs2XAgCl6 (X= Sc, Y) by applying the first principles approach. The confirmation of the stable structure of both compounds is reinforced by the negative values of formation enthalpies. The electronic band gaps (Eg) of 3.78/4.86 eV are computed for Cs2ScAgCl6 /Cs2YAgCl6 through Tran-Blaha modified Becke-Johnson (TBmBJ) potential, correspondingly. The tolerance factor(τ) is found as 0.9 for Cs2ScAgCl6 and 1.0 for Cs2YAgCl6 which confirmed the stable cubic nature of both compounds. Optical factors like dielectric-function ε(ω), absorption coefficient α(ω), and others related parameters are analyzed within 0 to 10 eV of energy span. Both compounds demonstrated high absorption in the ultraviolet region, rendering them as well-suited materials for photovoltaic applications. The calculated values of refractive index for Cs2ScAgCl6 and Cs2YAgCl6 indicated super-luminescent characteristics in the ultraviolet region. For thermoelectric (TE) features, electrical conductivity (σ/τ), figure of merit (ZT), power factor (PF), thermal conductivity (k/τ), and Seebeck coefficient (S) are calculated using the BoltzTraP code. According to the findings, both materials are advocated as promising candidates for thermoelectric and optoelectronic applications.

First-principles study on electronic, mechanical, and optical properties of pressure-induced vanadium-based perovskite KVO3

Vanadium-based compounds exhibit a variety of excellent characteristics due to their variable oxidation states. In this study, Density Functional Theory (DFT) is performed to investigate the structural, electronic, mechanical, and optical properties of KVO3 under high pressure. The thermodynamical and mechanical stabilities under high pressure are probed by the negative value of formation enthalpy and Born-mechanical stability criteria, respectively. KVO3 displays a nearly metallic nature in both pressurized and unpressurized systems owing to its remarkably narrow band gap. Furthermore, a positive pressure coefficient of the band gap is revealed from electronic properties. A lower effective mass value for charge carriers indicates KVO3's suitability for optoelectronic applications. The mechanical properties indicate that increasing pressure results in a slight increase in elastic constants, elastic moduli, hardness, and machinability index. Additionally, it has been disclosed that it is capable of enduring localized plastic deformation and fracturing under intense pressure in a prospective application. The calculations of the complex dielectric function, absorption, reflectivity, conductivity, refractive index, and loss function for KVO3 with and without pressure reveal a substantial behavior change. The absorption edge exhibits a significant blue shift with the applied pressure. The high peaks in the UV region suggest that it can be used in UV detectors and anti-reflection coatings. The refractive index shows promising application in waveguides.

Pressure-induced band gap engineering and enhanced optoelectronic properties of non-toxic Ca-based perovskite CsCaCl3: Insights from density functional theory

This study investigates the impact of hydrostatic pressure on the structural, electronic, optical, and mechanical properties of the cubic halide perovskite CsCaCl3. The pressure effect reduces the interatomic distance, which has a significant impact on this perovskite's lattice constant and unit cell volume. The electronic band gap narrows under pressure from the ultraviolet to the visible range, making it simpler to transport electrons from the valence band to the conduction band and increasing the efficiency of optoelectronic devices. Additionally, at around 50 GPa pressure, the band gap nature changes from indirect to direct, making the material better suited for use in optoelectronic applications. A deep optical study has shown that CsCaCl3 might be used in surgical tools, integrated circuits, QLED, OLED, solar cells, waveguides, and solar heat reduction materials. The mechanical stability of CsCaCl3 under the full range of applied pressure is confirmed by the elastic constants, which perfectly follow the Born stability criteria, the CsCaCl3 phase is proven to be stable across the whole applied pressure range by the tolerance factor "t", and support the thermodynamic stability achieved by the negative values of formation enthalpy. External pressure has a major impact on the mechanical properties, making this compound more ductile.

Modeling the thermochemistry of nitrogen-containing compounds via group additivity.

First-principles based kinetic modeling is essential to gain insight into the governing chemistry of nitrogen-containing compounds over a wide range of technologically important processes, e.g. pyrolysis, oxidation and combustion. It also enables the development of predictive, fundamental models key to improving understanding of the influence of nitrogen-containing compounds present as impurities or process additives, considering safety, operability and quality of the product streams. A prerequisite for the generation of detailed fundamental kinetic models is the availability of accurate thermodynamic properties. To address the scarcity of thermodynamic properties for nitrogen-containing compounds, a consistent set of 91 group additive values and three non-nearest-neighbor interactions has been determined from a dataset of CBS-QB3 calculations for 300 species, including 104 radicals. This dataset contains a wide range of nitrogen-containing functionalities, i.e. imine, nitrile, nitro, nitroso, nitrite, nitrate and azo functional groups. The group additivity model enables the approximation of the standard enthalpy of formation and standard entropy at 298 K as well as the standard heat capacities over a large temperature range, i.e. 300-1500 K. For a test set of 27 nitrogen-containing compounds, the group additivity model succeeds in approximating the ab initio calculated values for the standard enthalpy of formation with a MAD of 2.3 kJ mol-1. The MAD for the standard entropy and heat capacity is lower than 4 and 2 J mol-1 K-1, respectively. For a test set of 11 nitrogen-containing compounds, the MAD between experimental and group additivity approximated values for the standard enthalpy of formation amounts to 2.8 kJ mol-1.

Ga and In-based hybrid halide perovskites as an alternative to Pb: a first principles study.

Lead-free hybrid halide perovskites have gained much attention in the field of photovoltaics due to their non-toxicity, stability and unique photo-physical properties. Sn and Ge-based ABX3 perovskites have been widely studied due to their similar electronic properties to Pb-based materials. However, the unstable oxidation state of Sn is a major challenge for the commercialization of this class of materials. To overcome this problem, here, we have designed a series of novel Ga and In-based A3B2X9-type perovskite materials incorporating the methylammonium (MA) organic cation in the A site and I- as the halide ion in the X site. In this regard, we have investigated different structural, electronic, optical and photovoltaic properties by employing the density functional theory formalism. The formation of a stable three dimensional perovskite structure is determined by the observed values of tolerance factor (TF) and octahedral factor (μ). The observed negative values of formation enthalpy manifest that our studied materials are also thermodynamically stable. The obtained band gap values reveal that our designed perovskite materials can act as semiconducting materials for application in photovoltaics. We have also investigated the optical properties of our studied materials and the observed values of dielectric function and absorption coefficient in the visible range of the electromagnetic spectrum indicate their excellent photo absorption. The observed theoretical power conversion efficiency (PCE) values reveal that (MA)3In2I9 (13.82%) and (MA)3 (Ga.50In.50)2I9 (12.8%) can be chosen as potential candidates for application in perovskite-based photovoltaics. This research provides a pathway for the development of less toxic and efficient semiconducting materials, offering exciting prospects for their utilization in optoelectronics and contributing to the ongoing efforts to advance sustainable energy technologies.

Ab initio predictions of pressure-dependent structural, elastic, and thermodynamic properties of CaLiX3 (X = Cl, Br, and I) halide perovskites

In this comprehensive investigation, we undertook an ab initio exploration of the pressure-dependent structural, elastic and thermodynamic attributes of lithium-based halide perovskite compounds, namely CaLiCl3, CaLiBr3 and CaLiI3. Our analytical approach encompassed a diverse set of parameters, and the main conclusions and implications of our study are summarized as follows: (i) Calculated values of formation enthalpy and cohesion energy were determined for these perovskite compounds. Our results notably affirm the structural and thermodynamic stability of these materials in their cubic lattice configuration. (ii) Our optimized network parameters, derived from ab initio calculations, demonstrated commendable congruence with previously established theoretical predictions. This agreement strengthens the credibility of our conclusions. (iii) Using strain-constraint methodology, we successfully estimated the single-crystal elastic constants (Cij) of these compounds. This data served as the basis for further analysis. (iv) Using the obtained Cij values, we calculated a complete suite of elastic moduli for CaLiX3 (X = Cl, Br and I) in polycrystalline aggregates. This encompassed bulk modulus, Young's modulus, shear modulus, Lame coefficients, Poisson's ratio and Debye temperature, thus providing valuable information on the mechanical behavior of materials. (v) Using Debye's quasi-harmonic approach, we systematically investigated the temperature dependencies of several essential thermodynamic properties. These include the lattice parameter, thermal expansion coefficient, bulk modulus, Debye temperature, and isochoric and isobaric heat capacities. These analyzes covered a wide temperature range while maintaining fixed selected pressures. Overall, our study aims to provide the scientific community with a robust and comprehensive dataset regarding the structural, elastic, and thermodynamic attributes of CaLiX3 perovskite compounds.

Systematic investigation of magneto-electronic, structural, thermoelectric and optical properties of Nd2MgX4 (X = S, Se) compounds

The structural, magnetic, optoelectronic, and thermoelectric (TE) characteristics of Nd2MgX4 (X = S, Se) are determined by utilizing the density functional theory (DFT) based full potential linearized augmented plane wave (FP-LAPW) method as employed in WEIN2k code. The exchange and correlation energies along with Coulomb interactions are brought into consideration by employing local density of approximation with Hubbard model (LDA+U). Tolerance (τ) factor and formation enthalpy were utilized to confirm the stability of both spinels. τ values are 0.70 and 0.68, and formation enthalpy values are (ΔHf) are -3.34 eV and -2.19 eV for Nd2MgX4 (X = S, Se), respectively. For Nd2MgX4 (X = S, Se) metallic behavior is found in spin up case while considerable bandgaps are found in spin down with half metallic bandgap (Eg) values of 1.82 and 1.26 eV (in spin down), correspondingly. The calculated magnetic moment for Nd2MgX4 (X = S, Se) are 12.0008 μB and 12.0003 μB, respectively. Furthermore, optical features including refractive index n(ω), dielectric constant 𝜀𝜀(𝜔𝜔), reflectivity R(ω), optical conductivity σ(ω), absorption coefficient α(ω) and extinction coefficient k(ω) are computed. The maximum calculated real part of dielectric constant 𝜀𝜀1(𝜔𝜔) values for Nd2MgX4 (X = S, Se) are 9.2 and 10.8, respectively. For Nd2MgX4 (X = S, Se), σ(ω) has maximum value of 7642.9 at 6.6 and 7592.5 (Ω cm)-1 at 5.99 eV, respectively. The various temperature dependent thermoelectric (TE) parameters along with figure of merit (ZT) are determined to get full insight into the TE behavior for both compounds by using BoltzTraP code. The computed ZT value for Nd2MgSe4 is 0.81 at 800 K while Nd2MgS4 has ZT value of 0.80 at 800 K. Results showed that both spinels have potential in spintronics and in cooling industries.

Mechanical and thermodynamic behaviors of the second phases in Al–Zn–Mg–Cu alloys

The mechanical and thermodynamic behaviors of intermetallics in Al–Zn–Mg–Cu alloys are studied by first-principles calculations. All studied second phases have negative values of formation enthalpy and cohesive energy indicating their excellent thermodynamic stability. Al3Er_D0[Formula: see text] has the most significant metallic nature, while Mg2Si shows the least metallicity. TiAl3 shows the highest bulk, shear, and Young’s moduli. All Al3M polymorphs, Mg2Si and TiAl3 phases show covalent/metallic hybrid bonding. The mechanical anisotropic behaviors obey the trend of: MgZn[Formula: see text]Er_D0[Formula: see text]Sc_D0[Formula: see text]Sc_D0[Formula: see text]Er_D0[Formula: see text]Er_L1[Formula: see text]Sc_L1[Formula: see text]Si, where MgZn2 is the most mechanically anisotropic phase. The calculated room-temperature linear thermal expansion coefficient values for the studied phases are from [Formula: see text] K[Formula: see text] to [Formula: see text] K[Formula: see text]; where Al3Er_L12 has the highest value ([Formula: see text] K[Formula: see text], followed by Al3Sc_L12 ([Formula: see text] K[Formula: see text]; both of which are close to that of the Al matrix, thus making the relatively lower thermal misfit.

Revisiting the Thermodynamic Characteristics of Titanium Fluorides

New values for the standard enthalpies of formation of titanium fluorides at 0 K have been obtained by revisiting data on homogeneous and heterogeneous equilibria with their participation (kJ/mol): –1403.2 ± 2.7 for TiF3(c), –1144.2 ± 3.3 for TiF3, –2349.4 ± 6.3 for Ti2F5(c); –933.7 ± 6.8 for TiF2(c), and –650.4 ± 2.4 TiF2. The thermodynamic metastability of TiF2(c) has been shown.

Comparative Analysis of Physical and Chemical Properties of Differently Obtained Zn-Methionine Chelate with Proved Antibiofilm Properties (Part II).

The previously demonstrated activity of aqueous solutions of methionine and zinc salts against biofilms of uropathogenic bacteria prompted us to investigate the structure and properties of zinc methionine complex obtained from such solutions. The paper presents the analysis results of zinc coordination complexes with methionine obtained by synthesis (0.034 mol of L-methionine, 0.034 mol of NaOH, 40 mL of H2O, 0.017 mol ZnSO4, 60 °C) and simple crystallization from water solution (25 mL of a solution containing 134 mmol/L L-methionine, 67 mmol/L ZnSO4, pH = 5.74, I = 0.37 mmol/L, crystallization at room temperature during more than two weeks). IR spectral analysis and X-ray diffraction showed the structural similarity of the substances to each other, in agreement with the data described in the literature. DSC confirmed the formation of a thermally stable (in the range from -30 °C to 180 °C) chelate compound in both cases and indicated the possible retention of the polymorphic two-dimensional structure inherent in L-methionine with the temperature of phase transition 320 K. The crystallized complex had better solubility in water (100 to 1000 mL per 1.0 g) contra the synthesized analog, which was practically insoluble (more than 10 000 mL per 1.0 g). The results of the solubility assessment, supplemented by the results of the dispersion analysis of solutions by the dynamic light scattering method indicated the formation of zinc-containing nanoparticles (80 nm) in a saturated water solution of a crystallized substance, suggesting the crystallized substance may have higher bioavailability. We predicted a possibility of the equivalent existence of optically active cis and trans isomers in methionine-zinc solutions by the close values of formation enthalpy (-655 kJ/mol and -657 kJ/mol for cis and trans forms, respectively) and also illustrated by the polarimetry measurement results (∆α = 0.4°, pH = 5.74, C(Met) = 134 mmol/L; the concentration of metal ion gradually increased from 0 to 134 mmol/L). The obtained results allowed us to conclude that the compound isolated from the solution is a zinc-methionine chelate with the presence of sulfate groups and underline the role of the synthesis route for the biopharmaceutical characteristics of the resulting substance. We provided some quality indicators that it may be possible to include in the pharmacopeia monographs.

Investigation of X2CdS4 (X=Dy, Tm) spinels for energy harvesting and spintronic applications

The structural, electronic, magnetic, optical, and thermoelectric (TE) features of X2CdS4 (X ​= ​Dy, Tm) spinels are investigated by using the full potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). The stability of both materials is verified by the negative values of formation enthalpy (ΔHf) and tolerance factor. Both spinels are semiconductors with band gap (Eg) of 0.9/1.2 eV in spin up/down channels of Dy2CdS4, while Tm2CdS4 exhibits Eg of 1.04/0.80 eV in spin up/down channel. The calculated magnetic moments (μB) of spinels Dy2CdS4 and Tm2CdS4 are 19.000 and 8.00 ​μB, correspondingly. Optical features including absorption coefficient α(ω), refractive index n(ω), dielectric constants ε(ω), optical conductivity σ(ω), reflectivity R(ω), and extinction coefficient k(ω) are investigated. Both spinels X2CdS4 (X ​= ​Dy, Tm) discover the maximum photon absorption in the ultraviolet area, which proves that both are acceptable for usage in sensors, optical filters, and optoelectronic applications. BoltzTrap code is utilized to discover TE features like electrical conductivity (σ/τ), Seebeck coefficient (S), thermal conductivity (k/τ), power factor (PF) and figure of merit (ZT). Outcomes of this work enlighten the promising applications of studied spinel compounds in spintronic, optical and TE devices.

Magnetic, optical, electronic, structural and thermoelectric features of A2MgS4 (A=Sm, Tb): A DFT study

The spinel A2MgS4 (A = Sm,Tb) sulfides were analyzed by first-principle using the WIEN2k software based on density functional theory (DFT). Dynamic stability has been adequately explained using enthalpy of formation values (ΔHf) (−3.50 for Sm2MgS4 and -3.57 eV for Tb2MgS4). By examining band structure (BS) with spin polarized density of states (DOS), it is confirmed that Sm2MgS4 exhibits half-metallic ferromagnetic (HMF) behavior whereas Tb2MgS4 has semiconducting nature with a bandgap (Eg) of 1.56 in spin (↑) up and 0.94 eV in spin (↓) down channel. The estimated magnetic moments (μB) of sulfo-spinel Sm2MgS4 and Tb2MgS4 are 19.99931 and 24 μB, respectively. Transport properties such as thermal (k/τ) and electrical (σ/τ) conductivities, Power factor (PF), Seebeck coefficient (S), and figure of merit (ZT) are computed to determine the thermal behaviour of both spinels. From thermoelectric (TE) analysis, Tb2MgS4 maximum value of figure of merit (ZT) is 0.731 at 800 K, whereas the maximum S is 234 for Sm2MgS4 at 500 K and 267 μV/K for Tb2MgS4 at 350 K, hence, Tb2MgS4 is more efficient TE material than Sm2MgS4. Additionally, optical characteristics including absorption coefficient α(ω), extinction coefficient k(ω), dielectric constants ε(ω), reflectivity R(ω), refractive index n(ω), and optical conductivity σ(ω) are investigated. Computational results show that A2MgS4 (A = Sm, Tb) materials are potential candidates for spintronics, optoelectronics, and TE devices.

Predicting Enthalpy of Formation of Energetic Compounds by Machine Learning: Comparison of Featurization Methods and Algorithms

AbstractMachine learning (ML) is an emerging approach for predicting molecular properties. The prediction of the properties of energetic molecules by ML is still in its infancy. In order to improve the accuracy of ML‐based predictions, it is important to pay attention to aspects such as data preparation, model selection, and hyperparameter tuning. In this work, we focused on the influence of different featurization methods and algorithms on predicting the enthalpy of formation (EOF) of energetic compounds. We manually extracted a dataset consisting of 649 EOF values of energetic materials from the literature and compared different combinations of featurization methods and algorithms. The experimental results confirmed that ML can effectively map the relationship between molecular structure and EOF. Custom descriptor sets were found to perform best in featurization with a mean absolute error of 90.10 kJ mol−1, after training by kernel ridge regression algorithm.

Investigation of Alumina-Doped Prunus domestica Gum Grafted Polyaniline Epoxy Resin for Corrosion Protection Coatings for Mild Steel and Stainless Steel.

Eco-friendly inhibitors have attracted considerable interest due to the increasing environmental issues caused by the extensive use of hazardous corrosion inhibitors. In this paper, environmentally friendly PDG-g-PANI/Al2O3 composites were prepared by a low-cost inverse emulsion polymerization for corrosion inhibition of mild steel (MS) and stainless steel (SS). The PDG-g-PANI/Al2O3 composites were characterized by different techniques such as X-ray diffraction (XRD), UV/Vis, and FTIR spectroscopy. XRD measurements show that the PDG-g-PANI/Al2O3 composite is mostly amorphous and scanning electron micrographs (SEM) reveal a uniform distribution of Al2O3 on the surface of the PDG-g-PANI matrix. The composite was applied as a corrosion inhibitor on mild steel (MS) and stainless steel (SS), and its efficiency was investigated by potentiodynamic polarization measurement in a 3.5% NaCl and 1 M H2SO4 solution. Corrosion kinetic parameters obtained from Tafel evaluation show that the PDG-g-PANI/Al2O3 composites protect the surface of MS and SS with inhibition efficiencies of 92.3% and 51.9% in 3.5% NaCl solution, which is notably higher than those obtained with untreated epoxy resin (89.3% and 99.5%). In particular, the mixture of epoxy/PDG-g-PANI/Al2O3 shows the best performance with an inhibition efficiency up to 99.9% on MS and SS. An equivalent good inhibition efficiency was obtained for the composite for 1M H2SO4. Analysis of activation energy, formation enthalpy, and entropy values suggest that the epoxy/PDG-g-PANI/Al2O3 coating is thermodynamically favorable for corrosion protection of MS and exhibits long-lasting stability.

Investigation of X2GaAgCl6 (X = K, Cs) for Optoelectronic Devices: A Density Functional Theory Study

The electronic, elastic, structural, and optical properties of X2GaAgCl6 (X = K, Cs) are investigated by using the full potential linearized augmented plane wave (FP‐LAPW) method based on density functional theory (DFT). Generalized‐gradient approximation (GGA) is used along modified Becke–Johnson (mBJ) exchange potential. K2GaAgCl6 and Cs2GaAgCl6 reveal the direct bandgap (E g) of 2.57 and 2.63 eV, respectively, at Γ symmetry points. The negative values of formation enthalpy (−1.694 for K2GaAgCl6 and −1.798 for Cs2GaAgCl6) and value of tolerance factor (τ) close to unity (0.82 for K2GaAgCl6 and 0.89 for Cs2GaAgCl6) confirm the stable nature of X2GaAgCl6 (X = Cs, K) compounds in cubic phase. Optical properties such as absorption coefficient α(ω), optical conductivity σ(ω), reflectivity R(ω), extinction coefficient k(ω), refractive index n(ω), and dielectric constants (ε 1 and ε 2) are calculated. The ε 2(ω) spectrum of Cs2GaAgCl6 and K2GaAgCl6 shows highest absorption peaks at 4.8 and 4.9 eV, respectively. The highest absorption is observed from Cs2GaAgCl6 at 7.44 eV and from K2GaAgCl6 at 7.46 eV energies. It is also noted that A2GaAgCl6 (A = K, Cs) compounds are elastically stable, anisotropic, and ductile. Investigation of elastic, structural, and optical properties shows that the compounds M2GaAgCl6 (M = Cs, K) can be potential candidates for optoelectronic applications.

Improving Shear Strength of Ti/Mg Bimetal Composites Prepared by Hot‐Dip Aluminizing and Solid–Liquid Compound Casting

It is a great challenge to achieve the joining between Ti and Mg for their low solid solubility and positive formation enthalpy value. To fabricate high strength TC4/AZ91D bimetallic composite with metallurgical bonding interface, Al coating is prepared on the surface of TC4 alloy by hot‐dip technology, and Al‐coated TC4/AZ91D bimetal is prepared by solid–liquid compound casting herein. The effect of the hot‐dip process on the thickness and composition of the Al coating on the TC4 sample is discussed. Process parameters including casting temperature and liquid‐to‐solid volume ratio are investigated. The results reveal that the shear strength of Al‐coated TC4/AZ91D bimetal reaches 48.5 MPa when hot dipping at 700 °C for 15 min and casting at 720 °C with the volume ratio of 24, while that of the sample without Al interlayer is only 19.1 MPa. The reason is due to the formation of Ti(Al, Mg)3 intermetallic compound and Al12Mg17 + δ‐Mg eutectic structure at the interface. The results are helpful for the further development of high strength Ti/Mg bimetal by combining hot‐dip technology and solid–liquid composite casting technology.

Additive single atom values for thermodynamics II: Enthalpies, entropies and Gibbs energies for formation of ionic solids

In part I of this series we established optimised sum values, for each of the chemical elements, of formula volumes, of absolute entropies, and of constant pressure heat capacities, together with their temperature coefficients. These atom values, when summed for a chemical formula, provided zero-level estimates of the corresponding property of that chemical material. Atom sums have the particular advantage of being essentially complete because of the finite number of chemical elements and are of use in prediction and checking of values for chemical materials. However, this is at the expense of an inability to distinguish among isomers and phases with the same chemical formula nor do they allow for effects of atom interactions.In the present publication, we present optimised atom sums for formation entropies, formation enthalpies and their relation to formation Gibbs energies.In order to check the reliability of the results, comparison is made among methods of prediction using each of DFT calculations, a proprietary group contribution method, and the proposed single atom sum method. The single atom sum method is found to be most suitable as an initial estimate for large formation entropies and also for large values of formation enthalpies, which includes ionic hydrates.The energy contributions of the elements group into the Groups of the Periodic Table so that strict atom independence and thus additivity is not predominant while entropy terms are relatively constant (for the non-gaseous elements) implying that the atoms behave independently and thus additively in contributing to the entropy terms resulting from their vibrations within the ionic solids. This is possibly a unique demonstration resulting from this single atom sum collection.This now comprises a complete set for simple zero-order thermodynamic prediction and for checking, which should be complemented by whatever other resources are available to the researcher.